implementation module Snug.Syntax

import qualified Data.Set
from Data.Set import :: Set
import StdEnv

none = 'Data.Set'.newSet

instance usedSymbols [a] | usedSymbols a
where
	usedSymbols xs = 'Data.Set'.unions (map usedSymbols xs)

instance usedSymbols (a, b) | usedSymbols a & usedSymbols b
where
	usedSymbols (x,y) = 'Data.Set'.union (usedSymbols x) (usedSymbols y)

instance usedSymbols CaseAlternative
where
	usedSymbols (CaseAlternative pat expr) =
		'Data.Set'.difference (usedSymbols expr) (usedSymbols pat)

instance usedSymbols Expression
where
	usedSymbols (BasicValue _) = none
	usedSymbols (Symbol sym) = none
	usedSymbols (Constructor _) = none
	usedSymbols (Case e alts) = usedSymbols (e, alts)
	usedSymbols (ExpApp e1 e2) = usedSymbols (e1, e2)

instance usedSymbols Pattern
where
	usedSymbols Wildcard = none
	usedSymbols (BasicValuePattern _) = none
	usedSymbols (IdentPattern id) = 'Data.Set'.singleton id
	usedSymbols (ConstructorPattern _ syms) = 'Data.Set'.fromList syms